Group 21 2012 Gate 3

Using what we have learned in class, in this gate, we will be analyzing our bicycle\'s components as well as develop a functional model and analyse it at a subsystem level. Seeing as this product is already dissected, we will be able to analyze it in great detail.

We will first be talking about how our group works together and functions as a whole. We will then move on to talk about our product in a subsystem and component level. This will entail our bill of materials, product analysis, some 3D modeling, engineering analysis, as well as some design revisions of the product.

Project Management: Coordination Review

A big part of this project is to teach how to deal with working with other group members. It is important to realize what role one takes in a group to create the most efficiency. While being in a group brings in many different personality types, to be a successful engineer, we need to learn what to do when we have an issue with another person and how to deal with it.

Cause for Corrective Action

Even with the corrections made in the last gate, we are still having problems with the group.

\'\'Challenges\'\'

In the last gate we had the following major challenges:

Communication

Wiki Organization

Attendence

\'\'\'Challenges That Have Been Addressed\'\'\'

\'\'\'\'\'Communication\'\'\'\'\'

The main communication problems were as follows:

Primary mode of communication was text messaging.

Miscommunication of assignment due dates.

These were addressed by adding more modes of communication.

Emails are sent out weekly containing agendas of the meetings, due dates, new meeting times, etc.

We have set up a photobucket.com account so all pictures will be available for anyone in the group to access.

We have set up google docs account so all material being worked on will be available to each group member.

We have meetings about once a week and the minutes can be found in the table below.

Our progress in our Project Timeline as well as our meeting minutes can be seen in our Project Management page.

\'\'\'\'\'Wiki Organization \'\'\'\'\'

In our first gate, we were marked down highly because of our disorganization of the wiki page. We have changed roles and Tiffany has taken over the wiki programming. Comments from the grading rubric have been taken into consideration while this gate was being produced.

\'\'\'Unresolved Challenges\'\'\'

\'\'\'\'\'Attendance \'\'\'\'\'

A recurring problem we have been having as a group is the poor attendance not only to the weekly meetings, but to class as well. To solve this problem, we attempted to have a meeting with the professors that not everyone in the group attended. We address this as an unresolved challenge even through we have attempted to solve this problem a few times before.

We address this problem by sending emails to the professors, making them aware of the issues we are having. The emails contain all information covered in our meetings as well as who attended, who did not, the agenda of the meeting, time, place, etc. If needed the group member will be spoken to by the professors if they fail to meet the needs of the group.

\'\'\'Future Challenges\'\'\'

Some challenges we foresee are:

Group members still not attending class and/or meetings.

Group members refusing to participate.

Group members continuing to hand in late work.

Group members resigning the class.

If any of these situations occur we have the following solutions:

Group members who fail to perform will be penalized in the group evaluations.

For the upcoming gates there will be a due date for all gate parts, which will be split up among the group members. This due date will give the group members who participate enough time to pick up the slack if a part is not finished. The group members who do not participate and fail to hand in their part before the due date will not be asked to participate in the next gate. The professors will be alerted of the group members who were unwilling to meet deadlines and/or participate.

Product Archaeology: Product Evaluation

This part of the project is helping develop the design and analysis skills of each group member. This includes analysis of the product containing equations, dimensions, materials, interactions as well as design revisions of the product. We will see how each of these are important to decision making during the engineering process.

Component Summary

In order to properly analyze all the necessary parts and mechanisms to our system we fully dissected our bicycle and examined all the necessary components. Pertinent information included purpose, quantity, used materials, manufacturing processes used, part numbers, and other useful information. Information was gathered upon physical observations and close research. Information regarding the manufacturing processes used was taken from the in class supplement given. Examples include riser marks, parting lines, and undercuts. Other information was also gathered from other research such as the manufacturing process for sprockets, where metal is stamped using a die to cut, shape, and form the proper pieces. All hardware was recorded and the purpose of each was listed. As displayed, no system can properly work without a properly organized and placed set of components and subsystems.

A bill of materials, or BOM, consists of all the components of a product, as well as sub-assemblies, and the quantity of each needed to manufacture the end product. It is used as communication between engineer and manufacturer. It is referred to during manufacturing process, the design stage and again during sales and marketing. All information can be found in Table 2.

\'\'Table 2: Bill of Materials\'\'

Item/System Number

Name

Function

Material

Manufacturing Process

Quantity

Components

Picture

1

Pedals

place where the force is transferred to the crank; grips to the riders shoes

metal and plastic

injection molding

2

N/A

Pedals

2

Crank Arms

increases the mechanical advantage and direction of motion of the force

steel

die casting

2

N/A

Crank Arm

3

Crank Assembly

transfers all energy from the rider to the front sprocket

Steel and aluminum

die casting

1

one axle shaft: die casting

two roller bearings

one retaining nut (steel) with one retaining ring (aluminum)

two 14mm nuts to hold the two crank arms on

two pedals

One Axle Shaft. Part of Crank Assembly.

4

Front Sprocket Assembly

transfers the rotational force of the crank to the chain and increases the mechanical advantage depending on the sprocket in use

aluminum

metal stamping

1

N/A

Front sproket assembly located on front wheel.

5

Tires

allow the bicycle to ride smooth and hold traction

rubber

rubber mold

2

N/A

Tires and rims

6

Rims

hold the tire and create a surface for the brake pads to grab hold of

aluminum

starts with a lump of aluminum, which is then pressed through a template to create a profiled extrusion. The profile is then cut to length, rolled into a hoop, and joined

2

N/A

see above

7

Rear hub/sprocket assembly

transfers the kinetic energy from the chain to the wheel. Also changes mechanical advantage using sprockets

aluminum and steel

metal stamping and die casting

1

uses two 15mm nuts with washers (steel)

caption

8

Seat

provides a comfortable place for the rider to sit.

Rubber, foam, and steel.

include a rigid seat of a molded, nylon-based plastic. The seat is then covered with some sort of padding and wrapped in a easy to clean cover.

1

N/A

Seat

9

Frame

provides a structure for all the components of the system to be mounted to.

steel

tig welded bent tubing

1

N/A

Frame

10

Handlebars

allow the rider to hold on to the bike and steer the bike.

aluminum

bent tubing

1

N/A

Handlebars

11

Handgrips

give the rider a comfortable place to securely hold on to the handlebars

rubber

injection molding

2

N/A

Hand Grip

12

Derailleur

moves the chain onto different sprockets

aluminum, steel, and plastic

metal stamping and injection molding

2

N/A

Derailleur

13

Chain

transfers the mechanical energy from the front sprocket to the back sprocket

steel

metal stamped pieces are press fitted together

2

N/A

Chain

14

Kickstand

props the bicycle up when not in use

steel

cut and bent steel rod

1

N/A

Kickstand

15

Bike Levers

pull the cable to apply the brakes and increase the mechanical advantage to pull harder on the cable given a force from the riders hand

aluminum

molded

2

N/A

Brake Lever

16

Brake cables

transfer the energy from the brake levers to the braking mechanisms

braided steel cable in protective plastic sleeve

multiple drawn fine steel cables are combined for strength and protected by a plastic sleeve

2

N/A

Brake Cable

17

Handlebar clamp

holds the handlebars onto the steering stem

aluminum

die casting

1

uses two 6mm x 1.5" allen bolts

Handlebar Clamp

18

Steering stem

transfers the rotational force from the handlebars down to the front fork of the bike

aluminum and steel

die casted piece is welded to steel tubing

1

uses one 6mm x 6.5" allen bolt with an expansion nu

19

Gear selectors

plastic and aluminum

injection molded plastic levers riveted to a bent steel band

2

N/a

20

Gear selector cables

transfer the energy from the gear selectors to the derailleur mechanisms

braided steel cable in protective plastic sleeve

multiple drawn fine steel cables are combined for strength and protected by a plastic sleeve

2

N/A

Gear Selector Cable

21

Reflector

reflects light to provide a safer riding environment for the rider at night

aluminum and plastic

injection molded plastic riveted to a bent steel bracket

1

N/A

Reflector

22

Front/ Rear braking assembly

stops the bike using the friction between the rim and the brake pads

2

two brake pads (rubber and aluminum)

two return springs (steel): returns brakes to the "off" position

two 10mm x 1" steel bolts with washers: hold the braking mechanism to the frame

two brake arms: applies the force from the cable to the brake pads

four spacers (aluminum): keep the proper distance between the brake pads and the brake arms

two cable clamps (steel): attach the brake cable to the cable between the brake arms

Brake Pad

Return Spring

Bolts with washers

Brake Arm

\'\'Hardware Listing\'\'

one steel 13mm x 1.5" bolt with nut and washer (seat clamp)

two steel 15mm nuts with washers (hold front hub onto the front fork)

four 1/4-20 bolts with nuts (tighten clamps on both gear selectors and brake levers)

three 1/4-20 bolts (attach both derailleurs and the reflector to the frame of the bike)

\'\'\'Part Numbers and Prices\'\'\'

Product Analysis

Here we want to analyze some decisions we would make as an engineer if we were to design the product. We will answer the questions provided on Table 1 in the Gate 3 outline, justify the components we chose and tell how they are important to the user\'s experience.

\'\'Introduction and Justification\'\'

We will be identifying each component by their component number from the previous components list. Here we will identify the component and justify why we chose them to analyze.

\'\'\'Component #1- Pedals\'\'\'

The pedals are the component where the user turns it\'s signal into force which essentially drive the entire movement component of the bike. If there were no pedals on the bike, it would be much harder to apply the force to turn the chains which turn the back wheel, thus allowing the bike to move.

\'\'\'Component #5- Tires\'\'\'

The tires are the components that create the frictional force between it and the ground. Without this force, the rims would spin and spin and no movement would be created.

\'\'\'Component #6- Rims\'\'\'

The rims are used to hold in the tire as well as used for frictional forces for the brakes. Without this component, the brakes would not work as intended. Also, there would be no mechanism used to hold the tire which creates the frictional force required to drive movement.

\'\'\'Component #8- Seat\'\'\'

The seat allows the user to rest comfortably while riding. This part is essentially needed for social factors. Many users have bicycles as their primary mode of transportation. They are traveling long distances and want to be comfortable while using the product for long periods of time.

\'\'\'Component #9- Frame\'\'\'

The frame is the most important component of the bicycle. It holds all of the subsystems together so they can work as one.

\'\'\'Component #10- Handlebars\'\'\'

Handlebars help the user stabilize the bike. Not every user has the balance to ride the bike without using the handlebars. They make the product more socially acceptable and gives stability.

\'\'\'Component #13- Chain\'\'\'

The chain is the connector between pedals and back wheel. Without the chain, the bike will not move when the user exerts force on to the surface of the pedals, which defeats the purpose of the product in this day. In the past, a bike was used in this manner. With the new technology that has been developed throughout the years, we have found a more efficient way, thus the chain component.

\'\'\'Component #16- Brake Cables\'\'\'

The brake cable is needed for the brake pad to create friction with the rim. Without the cable, the braking mechanism on this bike would not function. Another braking mechanism would need to be added, or the user would have to put down their feet to stop the bike. The braking cables allows the user to slow down and stop safely.

\'\'\'Component Function\'\'\'

Here we will be talking about what components functions they perform, what flows they are associated with and what environment it functions in. We have discussed this concept for each component in Table 3.

\'\'\'Component Form\'\'\'

Here we will be talking about the geometry, material and appearance of the component. For geometry, the general shape, properties, how it influences the function of the component, weight, etc. For material, we will be talking about what the component is made of as well as manufacturing methods, which will include aesthetics. We have discussed this concept for each component in Table 3.

\'\'\'Manufacturing Methods\'\'\'

We will be specifying out manufacturing choices with evidence and conclusions coming from shape, material and GSEE factors. We have discussed this concept for each component in Table 3.

\'\'\'Component Complexity\'\'\'

We will define a meaningful scale to how complex our component is. We will also discuss the complex the connections. We have discussed this concept for each component in Table 3.

\'\'Table 3: Product Analysis\'\'

Bicycle Reference Picture

Component Number

Component Name

Component Function

Component Form

Manufacturing Methods

Component Complexity

1

Pedals

Allows the rider an easy area to apply force that will allow the bike to make a translation motion.

Connected by the axle arms which are then attached to the sprockets and chain.

Rider applies force downward on the pedal, torque is created, which turns the sprockets.

Moves the chain, which then moves the rear sprocket assembly.

This makes the rear wheel turn, and with the help of the friction force between the tire and the ground, creates a translating motion in the form on kinetic energy.

Need to be strong enough to withstand the force of a person as well as have enough friction so the foot does not slip off when the axle is rotating the pedals.

Need to be wear resistant as they are exposed to the environmental elements.

Shape of a rectangle.

Axis symmetric which helps with the distribution of the user\'s force.

Two dimensional.

Does not translate in z-direction (coming out of the page).

Can rotate about the z axis as well as translate in the x and y directions.

The component is 3"x4"x1", which is a good size considering the dimensions of the foot of an average human being.

Flat surface with some plastic ridges on it which helps keep the rider\'s foot from slipping.

Rider must push down and exert force to the top of the pedal.

Component is light weight because of the nature of the bike.

The user wants to be able to transport the bike easily, even when not being ridden, which means all components should be light weight.

Made from plastic.

Strange geometry because of the plastic grips made to create friction for the rider.

Could have been made out of metal, however this would have been more open to rusting.

Because of global factors, some users do not have the environment wanted to go mountain biking.

They must then transport the bike to another location.

The components are light weight to make it easier on the user to do so.

It has no real aesthetic purpose.

It is made out of plastic and is colored black, which may be more pleasing to the user rather than a translucent pedal.

Made by injection molding.

The geometry of the top surface of the pedal is irregular.

Material is plastic.

Injection molding was not the most inexpensive choice, but if another manufacturing process was used, more machine methods would be needed to create a top surface finish that would give efficient friction with the user\'s shoe.

The shape of the pedal is pretty complex.

The ridges and contours of the top surface that comes into contact with the user\'s shoe is hard to measure and get the exact dimensions of.

The overall function of the pedal is simple.

The chosen manufacturing method of injection molding also tells us that we have a complex component.

Simple components would be made with a manufacturing process that would be cheaper to mass produce.

The pedals are attached to the sprockets by an axle arm which is held on by a plastic cap.

Because none of these are permanent attachments, and the components that are touching the pedals are also simple, we see the pedal\'s interactions to be ordinary.

5

Tires

The component that come into direct contact with the ground.

The final connection to the output of the bicycle, and are what accelerate and move in the circular motion that translates to the desired linear motion of the rider.

Made of rubber, and need to be strong as they will come into contact with many other materials.

Circular in shape, which is complementary of the fact that they are directly and indirectly connected to the rest of the bicycle, including the gears.

The rider moves the pedals in a circular motion, which indirectly causes the wheels to rotate in a circular motion, which is translated to the desired linear motion.

Slightly larger than the rims, and are often classified by the diameter of the tires.

Weight is directly proportional to the air pressure in the tire, which can be modified by the user.

Made from rubber.

Rubber is an incredibly durable, flexible material that can withstand traveling over the terrain in all kinds of conditions.

Rubber is relatively affordable for the overall cost of the other components, thus making it a very popular choice based on economic considerations.

Rubber is so flexible-necessary for the tire to function properly.

Design is based mostly on function, and not on aesthetics.

Tires are black which matches most of the other components of the bicycle

The traction and friction factors of the tires far outweigh any possible aesthetic factors when it comes to something so important.

The surface of the tires are very rough

needs to make use of all the frictional force possible in case the user needs to stop or turn immediately.

This is also important in case the rider is in bad riding conditions, so the bicycle doesn’t slip.

Created from a rubber mold.

When placed in the mold, elevated pressures and temperatures are used to create the shape.

The tires are then cured and inflated, so they can be manufactured with the other parts.

This is the ideal process for rubber

as it is not bad for the environment

cheap way to machine it.

The shape of the tires are very elementary

a perfect circle.

They are constrained to the rims

which is very simple

The orientation of the tires is important when it comes to calculating efficiency between different types of bicycles.

6

Rims

The main function of the rims are to hold the tires and provide shape and support for tires.

provide a platform to support the brake pads

is imperative for the entire braking subsystem.

The flows that come in and out of the rims that perform multiple functions are the reactions from the forces of the bicycle being driven, the forces to support the tires.

The rims are in a circular shape

providing the shape for the tires

weigh less than a couple of pounds

The rims are a circular shape

are axis symmetric

have a slightly smaller diameter than the actual tire

measured in two dimensions

thickness only being needed for very technical details

made from aluminum

cheap, lightweight and machinable material

major economic factor

made through the extrusion process

can be machined easily

a strong and reliable material

very safe and has the strength to support the rider’s weight

resistant to a great amount of corrosion

global factor

attractive surface finish

silver color provides a good aesthetic touch

process that is chosen to manufacture the rims is chosen more for functional purposes.

The pieces of the profile are cut and joined with a nice finish, so they always look good when new.

The process to manufacture the rims is lengthy compared to other parts.

The aluminum is pressed through a template to make an extrusion of the desired profile.

The profile is then cut and rolled, and joined to finish the desired shape.

The thin shape of the rods is also what makes this manufacturing process appropriate for the rims.

This is an economically efficient process for aluminum that maintains the strength of the aluminum to provide good stability for the tires.

This is good for the safety concerns, and these processes are environmentally friendly compared to the alternatives.

The rims are slightly more complex than some of the other parts

The calculations to get the rims to be the proper width are very important

if they are too small or too large it would be very unsafe.

The tires would not be aligned with the rims

they could fall off after a certain point of traveling

They are constrained to the tires rather simply

their sizes have a direct relationship

8

Seat

provides a stable position for the rider to sit

can balance themselves

directly connected to the frame by a steel rod

like the frame it provides support for the rider

When the bicycle experiences slight changes in elevation due to hitting bumps or going up hills, a force is applied between the rider and the seat.

opposite force coming from the seat supports the rider, working in conjunction with the frame

Bicycle seats are symmetric

have different designs for men and women

Designs vary based on the brand of bicycle

They are three dimensional

are between six to eight inches long, and 5 to 7 inches wide

an be adjusted to provide better support for riders of different heights

The shape is designed to be comfortable for the rider

weighs 1-2 pounds

Bicycle seats are made out of rubber

with foam padding

connected to the frame by a steel rod

The seat needs to be firmly connected to the frame which is made out of steel

When the seat can be adjusted, the rods often slide up for down so the height can be adjusted.

Rubber and foam are also good choices for the seat

cheap

economic factor

they make it comfortable for the rider

are soft but durable

The foam is there strictly for comfort

the rubber is made to resist all harsh weather conditions.

A global concern is that the bicycle can be used in the rain, so rubber is a good choice for the seat as the rain will not damage the seat.

The steel rod contributes a safe, strong connection to the frame

an important safety factor

Its overall purpose is to provide support and stability

making it look good is important to a variety of designers

The seat is black

very smooth and comfortable

The seat is based off a molded, nylon based plastic.

It is then wrapped in a padding then covered.

This is apparent due to the unique shape and the material.

this process is economically cheap and not bad for the environment compared to the alternative methods possible

The fact that the component is so sturdy and reliable is a big safety factor for the product.

The seat is a very simple component.

The adjustable rod is also very simple

it is connected to the frame so that it can be easily customized by the rider

The placement of the foam under the rubber seat is moderately complex, as it must be positioned in the most efficient possible way to preserve costs and efficiency.

The materials for the seat are very efficient

9

Frame

It provides a base for several other components to be attached to.

It also acts as a structural base for the rider

the design and properties of the frame are extremely important when designing a bicycle

Flows that come into the frame are kinetic energies along with energy relationships with the connected subsystems.

The frame can function in all environments

never comes into contact with the ground

material makes it not greatly affected by the rain

The frame has steel bent tubes that are positioned at certain angles relative to each other

provide ideal structural support

Frame is approximately three feet in total length and a foot and a half in height

Frames are measured in three dimensions

all three dimensions contribute to unique properties of the entire bicycle

The diamond frame is the most common design today

Modern frames can also be much more sophisticated with implementation of suspension systems

weigh between 20 and 30 pounds

made out of steel

Steel is a very strong

reliable material

found everywhere

There are alternatives to steel for bicycle frames

They are often made out of aluminum

cheaper and less reliable alternative

Carbon fiber

high quality

more expensive alternative

A global factor that influences the choice of material is the resistance of the material to corrosion in harsh weather conditions as they change around the world

The frame being small and lightweight is due to a societal factor or safety in case the rider falls over while using the bicycle

Cost is always a factor when choosing the material for any component in a bicycle

Steel is a good combination of economic efficiency and performance efficiency for the frame of a bicycle

An environmental concern with choosing steel for bicycle frames is that it is bad for the environment in the production process.

This could lead some people to wanting to use an alternative material for the frame.

Aesthetics are important when it comes to a bike frame.

A lot of time and effort is put in to creating ideas for designs and colors of bicycle frames

often to express differences between different brands of bicycles

This is another reason why steel is a popular choice

it leaves an aesthetically pleasing outer coat that can have many types of designs on it.

There are also functional reasons why steel is a good choice for a frame.

It is designed to be resistant from corrosion and to be able to withstand a variety of bad weather conditions.

The bicycle frame was made from welded bent tubing.

This is apparent because of how the frame looks where the bars are connected.

an easy way to join steel parts

ideal way to connect the bars at the desired orientation due to the nature of their shapes

form a reliable joint between the bars

economically feasible way to do this

The fact that the joints are so reliable and strong is a safety factor in society.

These bonds will hold strong in weather conditions all over the world, which is a global factor today.

Welding is an efficient process with minimal negative effects to the environment relative to alternative choices.

The geometry of the frame is derived from complex calculations that take into effect contributions from:

intended size of the rider

weight

type of bicycle

The frames connections to the seat, handlebars, pedals and wheels are very simple

serves as a platform to connect almost everything else present on the bicycle

The material of the bicycle is very strong

can support these interactions between the components

a very simple component which only has simple connections to other components.

10

Handlebars

They serve as a support to the rider

steer the bicycle when the rider shifts their hands

can be explained by the flows that go in and out of the handlebars

The rider sees something that they have to react to, and they move their hands in a simply intuitive process that changes the position of the bicycle.

The handlebars function in all environments

they should function appropriately as long as the terrain one is riding in isn’t too rough or slippery

The handlebars extend up from the frame of the bicycle

split out so the rider can position one hand on each handlebar

handlebars are symmetric perpendicular to the length of the bicycle frame

makes it convenient for the rider

a three dimensional object

they stick out six to eight inches from the perpendicular bicycle frame

The intuitive design of the handlebars is imperative to the overall design

The rider can pull their left arm back to go left, or their right arm back to go right.

This is made possible because of the design of the handlebars.

They are very lightweight

weigh 2-3 pounds

The handlebars are made out of aluminum

Many factors play a role in the design of the handlebars.

Aluminum is an ideal material for the handlebars because of the relative cost and machinability of it.

The strength and reliability of aluminum in all types of weather conditions around the world is a global factor that contributed to the design of the handlebars.

The strength and reliability are also a safety factor.

The intuitive design of the handlebars are also a societal and safety factor.

The fact that aluminum is cheap and very machinable is a huge economic factor.

One argument against the use of aluminum is that it is not an environmental friendly material.

However, there are not a great amount of alternatives that are of relative cost.

Aesthetics are not as big of a factor in the handlebars of a bicycle as some of the other parts.

The most important thing is that they are designed in a comfortable position for the rider so that they have complete control over the bicycle.

Grips are often placed over the handlebars to provide better control for the rider.

Those are a different component and a different material, and have more functional purpose than aesthetics.

The handlebars were made by the process of tube bending.

This is possible because they are made of aluminum, which is more machinable than the alternatives.

Titanium and carbon fiber are more expensive alternatives.

The length and shape of the handlebars enable them to be made by this process.

This process is good for the environment as opposed to the alternatives and it is a cheap process the produces reliable and strong handlebars, which is essential to the bicycle functioning properly.

The handlebars are again a very simple component relative to the other components of the bicycle.

They were designed based on an intuitive model that is a safety factor for all riders.

They are connected simply to the frame in a comfortable position for the rider to be able to use them effectively.

The are directly connected to the direction of the wheels, which is again intuitive for the rider.

Overall, the handlebars and their connections are all very simple.

13

Chain

It\'s function is to translate the force given by the rider on the pedals to kinetic energy from the sprockets and rear wheel by torque and friction from the ground.

It also helps the bike shift.

If the chain is on a higher sprocket on the rear wheel, it is in a lower gear.

The chain is also exposed to all the elements, (i.e. rain, snow, puddles of water, mud, etc.)

it is required to be made out of a material with high tolerance to corrosion

The general shape of the chain is numerous circles connected.

The circles are asix- symmetric, which makes the chain moving on the sprockets easier.

It rotates around the z axis and also translates around the z axis.

This component is mostly one dimensional.

When our reference frame is the bike, the chain is not moving up and down or left and right.

It does however, move when shifting.

When the chin is stretched out between the two sprocket assemblies, (rear wheel and pedal axle) it is about 12" long and 0.5" thick.

The chain has space between the circles which allows the sprockets to fit in.

This helps the function of the chain immensely.

Without this space, the chain would not be able to connect the two mechanisms that are so important to translating the forces to kinetic energy to allow the bike to move.

The chain is one of the heaviest components on the bike.

This is because of the material it is made of as well as it\'s need to be strong enough to withstand the forces being applied to it.

The chain is made from steel.

Again this is needed because of the forces it needs to withstand.

Steel is very strong and will enable the chain to transfer the mechanical rotations from the pedal sprockets to the rear wheel sprocket assembly without breaking or failing.

This is influenced by economical factors.

User\'s do not want to spend time and money fixing their bike numerous times.

The chain is made out of a durable, strong material so the chain is more likely to withstand the life of the bike.

This will decrease maintenance costs.

There are not many aesthetic properties of the chain.

It is not there to look pretty, it is there to drive the bike.

It is a dark grey because it is made from steel.

It is also a dark grey because it seems like the previous owner has gotten much use from it.

There is mud and dirt that has not been cleaned off.

The surface finish, before the bike was used, was a fine surface finish.

This was to make the bike more appealing to the purchaser.

The chain is made by the metal stamped pieces being connected by press fitting.

There are many of the same shapes in this component which leads us to believe it was manufactured this way.

The material must be soft while being stamped or there could be splitting and surface imperfections.

Also, the shape of the circles and the geometry being so simple allowed the process to be done over and over, allowing the pieces to be easily mass produced.

The part being able to be massed produced is a very important economic factor.

It is cheaper if done this way rather than die casting or using injection molds.

The chain is a mass produced product.

It\'s full geometry, however, is a bit more complex because of the number of parts it is compiled of.

The function, again, is fairly simple, but only because our product of the bicycle has very simple mechanisms.

For these reasons, we see the chain to be an ordinary component.

The components the chain interacts with are also simple.

Both sprockets (pedal and rear) are basically the same just different size.

The chain fits perfectly onto the sprockets and rarely fall off without the help of an outside force.

For these reasons, the interactions of the chain are also ordinary.

16

Brake Cables

The brake cables are the component that is used to send the signal from the user to the brake pads.

Without this, there would be no braking in an emergency.

The rider would have to find another way to slow down and/or stop in an emergency.

The user sends it\'s signal to the front brake levers.

The force exerted on the levers pulls on the cables which run down to the brake pads located on the rear and front tires.

The cable being pulled allows the brake pad to close onto the rim, thus creating the friction needed for the bike to slow down and/or stop completely.

The cables are made out of steel, but protected by a plastic sleeve.

This component is also exposed to the elements of nature.

The plastic casing helps with protecting the steel from rusting.

The general shape of the component is a cylinder.

It is axis-symmetric about the cross sectional area of the wire.

It is primarily one dimension when considering the flow.

The brake lever is pulled which pulls the wire (in one direction only).

The wire does not rotate about any axis.

The wire is about 12" long for the front and 36" long for the back.

These lengths are needed to cover the distance from the brake levers to the brake pads located on each wheel.

The cables are very light weight.

They are made out of steel but are so thin that they are not heavy and do not weigh down the bike.

Cables are made from steel so they will withstand the life of the bike.

They are a very hard component to replace seeing as you would have to cut them to fully remove them from the bike.

If they are needing replacement, you are probably better off purchasing a brand new bike.

Having the brake cables are directly from a societal factor.

There are other ways to slow down and stop a bike\'s movement.

Users want an easy, low maintenance way of doing this.

Before the cables, users would put their feet down and use the friction between their shoes and the ground to stop their motion.

This method was more expensive.

The steel cables are covered with a black plastic for aesthetic reasons.

They are also latched on to the frame for aesthetics.

The black plastic covers the color of the steel, helping the cords match the bike more properly.

The surface finish is fine and smooth to not be caught on the user\'s leg while riding.

The black plastic also protects the steel from rusting.

To produce the brake cable, a deep drawing process is used on each of the steel pieces.

We can tell this process was used because of the uniform axis symmetry of each strand.

The die was used to produce each piece.

Each piece was then braided together and combined for strength purposes.

This method was used to reduce maintenance needed.

The stronger the cable and the more protected it is, the longer the life cycle of it.

Thus, maintenance cost on the bicycle will go down.

This is a very important economic factor that allows the bicycle to be affordable to most customers.

The plastic on the outside of the cable is also added for economic purposes.

It protects the steel from mud, water, etc., which helps on increasing the life of the bike and decreasing the needed maintenance.

The brake cables is a product that can be mass produced for fairly cheap.

The material used is also a common material (both plastic and steel).

The geometry of the cable is widely used.

The dimensions can easily be measured by hand.

The functional flow is a bit harder to follow and understand.

The distance the cable moves from the lever is the same distance needed to move the brake bad so it is touching the rim of the wheel.

For these reasons, we believe the component is ordinary.

Also for the reasons stated above, the interactions between the cable and other components are ordinary.

Solid Modeled Assembly

As one of the most important parts of a bicycle, the mechanical system chosen here is the crank assembly. Without the crank assembly, there would be no way to transfer energy from the rider to the bicycle. It is the component of a bicycle drive train that converts the reciprocating motion of the rider\'s legs into rotational motion used to drive the chain, which in turn drives the rear wheel. It consists of one or more sprockets attached to the cranks, arms, or crank arms to which the pedals attach. It is connected to the rider by the pedals, and to the bicycle frame by the bottom bracket. Cranks are constructed of either an aluminum alloy, titanium, carbon fiber, chromoly steel, or some less expensive steel. This may be the single most important mechanical system on a bicycle and is important to understand thoroughly.

\'\'Crank Axle\'\'

The crank axle is a rotating shaft encased in a tubular mount. The shaft rotates within roller bearings inside the mount. The tubular mount is welded onto the frame of the bicycle. In the above diagram, the crank axle is the symmetric white shaft located inside the outer tubular mount. The roller bearings are depicted by the four white circles which ride on the outer grooves of the crank axle. This piece connects the left and right crank arms.

2D drawing of the crank axle

\'\'Crank Arms\'\'

Cranks arms are attached to either side of the crank axle typically by either using threaded holes or a keyed or shaped hole tightened into place using nuts that thread onto the outer ends of the crank axle. This is the case on our bicycle. The arms are mounted 180 degrees apart from each other. The opposite ends of the arms are then "attached" to the rider by the pedals. Crank arms can technically increase the mechanical advantage of the crank assembly. A longer crank arm produces more torque but, too long of an arm does not allow the rider to pedal quickly enough due to the rider having to pedal in a larger circular motion.

3D drawing of the left crank arm

3D drawing of the right crank arm

The difference between the left and right crank arms is that the right arm has five mounting brackets to which the front sprocket is attached using bolts.

\'\'Sprocket\'\'

The front sprocket is how the rotational motion is transferred from the crank assembly to bicycle chain. The bicycle chain the turns the back wheel.

2D drawing of the sprocket

Engineering Analysis

\'\'Component\'\'

The frame is a key component of the bicycle. It is the backbone, which supports and connects all of the other parts. It also contributes to a large percentage of the bicycle’s weight, which is a huge factor in a bicycle’s performance. Lastly, the frame plays a big part in determining the final cost of the product since different frame materials are more expensive than others. To a consumer, those are the two biggest concerns: performance and cost. For these reasons, it is a component that would require a lot of engineering analysis during the design and testing stages of the design process.

\'\'Analysis Process\'\'

\'\'\'Problem Statement\'\'\'

Engineers first need to determine the problem to be solved. In this case, the problem is deciding the best material to be used in the bicycle frame. To begin, certain questions need to be asked. Who is the target audience? Are they a casual or competitive rider? Are they male or female? What is their weight and height range? They also need to know what the factors are that decide performance and make one material better than other. What are the equations that are used to determine that?

\'\'\'Diagram\'\'\'

First we must understand the loads that the bicycle frame is subjected to and must be able to withstand. The following system diagram is helpful to visualize it:

There are two main factors, stiffness and strength, that determine how well the frame is able to support these forces. These two factors, along with the main design factor, weight, all affect the general performance of the bicycle and must be taken into consideration during the design process. The ideal frame has a high stiffness so that it can support the mentioned loads with minimal elastic deflection (bending). It has a high strength to avoid cracking and fatigue due to impacts and rough surfaces, and it has a low weight so that it can accelerate and go uphill faster (“aluMATTER”).

\'\'\'Assumptions\'\'\'

Depending on the audience, different assumptions can be made. For example, if the audience is a child, it can be assumed that cost will be a big factor, since children grow out of bicycles quickly and need to replace them more often than an adult. It can also be assumed that the child won’t take care of it very well, and get in a lot of damaging collisions and impacts, therefore it will also need to be strong enough to withstand those impacts. This is why knowing the audience is a big part in analysis, and is one of the first questions asked.

\'\'\'Equations\'\'\'

Different materials perform better than others in tests for these factors.
We must also take into account the fact that some materials weigh more than others, so stiffness and strength need to be based on a strength-to-weight ratio and a stiffness-to-weight ratio. For example, aluminum weighs less than steel, but a tube of aluminum is less stiff than the same exact same size tube made of steel. Aluminum can be stiffer than steel though if the diameter of the aluminum tubing is increased. Of course this would increase the weight, but compared to the steel, it already weighs a lot less, so the extra weight is allowable (“Ultracycling”). For this reason weight is taken into account in stiffness and strength by dividing by the material density. The following equations are used to determine the specific stiffness and specific strength for different materials (“aluMATTER”):

Stiffness equation used for analysis

The formula for stiffness is based off of the elastic beam theory and the following equation for the deflection of a beam:

Deflection equation used for analysis

\'\'\'Calculations\'\'\'

Using these equations, we can then calculate the values for different materials to see which ones will perform better. The specific stiffness and specific strength (fatigue resistance) for different materials common materials are plotted below. The materials highlighted in blue are materials that have been used in bicycle frames already (“aluMATTER”).

This chart shows that carbon fiber reinforced plastic (CFRP) is the material that will provide the best performance as it has a high stiffness and strength (fatigue index) while also providing a minimal weight. This makes sense because CFRP is known to be very light and very strong, which is why it’s a great alternative to the common steel frames. Notice also that the metals all have roughly the same stiffness, but vary in strength, with titanium and magnesium being stronger than steel and aluminum, which makes sense if you think about common objects made from each of those materials.

\'\'\'Discussion\'\'\'

While CFRP is the better material, it is also very expensive. Steel on the other hand, is known for its strength but relatively low cost, which is why it’s still used widely in bicycles today. It would probably be the best material to be used in a bicycle aimed for children. Engineers will need to build different bicycles with different materials to satisfy a range of audiences. Engineering analysis is used to determine the best design for a specific audience, and what tradeoffs will need to be made to accommodate that audience. For example, a casual rider that uses a road bike will not care as much for performance and care more for cost, so in the analysis, the engineer will have to sacrifice performance for cost. The opposite can be true. A more competitive rider who cares most about speed and performance will want the best material and care less about cost. Bicycles targeted for that audience, will have a more expensive, yet better performing frame. The analysis process will need to be used to determine exactly what the audience is, and what kind of tradeoffs need to be made to satisfy them.

\'\'Aesthetics\'\'

Lastly, in the design process, engineers have to appeal to the eye of the consumer. The color, the size, and the overall external appearance are all still important to the consumer, as well as performance and cost. A flashier and sleeker bike will look more attractive and most likely sell better.

\'\'Targeted Audience\'\'

What the engineer chooses for the final design all depends on the targeted audience. For example, with our product, the targeted audience seems to be casual riders that want a low cost bicycle and don’t seem to care too much about performance. This can be concluded by the fact that the frame is made of steel, which doesn’t perform as well as other materials, but is relatively cheap. It can also be reasonably concluded that it is targeted to female consumers since the color of the frame is baby blue. These are all factors that an engineer needs to take into account for analysis during the design process. Tradeoffs will always have to be made in order to satisfy different audiences.

Design Revisions

\'\'Pedal Axle\'\'

The first component that would undergo design changes is the Pedal axle, or the axle in which the pedals rotate about. The main problem with the existing pedal is its near impossibility to replace or repair. While the part will remain in the bicycle (which is a good thing), it the owner needs to repair or replace a broken axle he/she will find it impossible to do so (which is not a good thing). We propose adding a locking mechanism that would hold the axle in place during use, but could be disengaged to allow for quick and easy maintenance. This solution will drastically increase serviceability, and as a result, will mean less bikes will need to be bought when they can be more easily repaired, which addresses economic concerns.

\'\'Pedals\'\'

The next pedal that will need replacing is the pedals themselves. The existing pair are a tad to large and are heavy. We propose replacing them with a pair of much lighter weight plastic pedals. While the durability of plastic is less than that of the steel pair, they are not susceptible to rust and are not subject to the standard wear and tear on the rest of the bicycle, and as a result, the loss in durability is negligible. By reducing the weight, and the price, this addresses both social and economic concerns by allowing the bike to be more accessible to a larger market.

\'\'Bottle Holder\'\'

While not an essential part in the operation of the bicycle, it is still an important user accessory. The current component is extremely loose and does not effectively hold bottles. A simple swap with a different model would provide a much more effective and reliable way of holding bottles. This addresses the societal factors in that it increases the comfort of the rider by providing him/her and easy source of water.